Iorveth (Iorweth in the original Polish) is an elf, a well-known hater of humans, responsible for burning many human villlages and civilian deaths, and was the commander of the last Scoia'tael commando to be broken during the second war with Nilfgaard. One of the elves under his command was Echel Traighlethan who was captured by the Redanian Secret Service and brought to Drakenborg to be hanged.

The Witcher 2: Assassins of Kings

Spoiler warning: Significant plot details follow.
The character of Iorveth , despite being named from one character from the novels, is clearly modelled on another, Isengrim Faoiltiarna. He first appears in the cutscene on the beginning of the Chapter I of the game. It depicts what happened at about five months before the time of the game. He's approached by a mysterious individual claiming to be a friend of nonhumans with an offer: the man wants to kill kings for his own inscrutable reasons, and would like Iorveth's help in form of the elf's knowledge of secret trails and weapon stashes. To back his claim, this man shows Iorveth a head of Demawend, King of Aedirn and Sovereign of the Pontar valley.

At the beginning of Chapter I, Geralt, Triss and Vernon Roche meet Iorveth. Roche appears to know the elf and they are quite hostile to each other, hinting at less-then-pleasant past experiences. Shortly afterward, it becomes clear that Iorveth managed to rebuild the commando he lost during the war, as elves attack Geralt and company on his orders.

He is pushed by circumstances to the very edge of society, painfully aware that the Scoia'tael have been used in the war with Nilfgaard and have been ruthlessly sacrificed during peace negotiations. And he is determined not to let that happen again. He enjoys a fierce loyalty from his men. None of them would ever betray Iorveth and this speaks volumes in his favor. Indeed, he is a skilled commander and as cunning as a fox.

Considered a mass murderer and terrorist, even by Saskia, he has nontheless come to understand that the ways of the Scoia'tael are doomed to fail, hence the reason he did not join Yaevinn and instead chose to fight side by side with humans and dwarves to secure the foundation of an independent state in Upper Aedirn. A state with egalitarian laws between elves, humans and dwarves.